1. Field of the Invention
The present invention relates to an optical element supporting device for information recording/reproducing apparatuses. The optical element supporting device supports an optical element included in an information recording and/or reproducing apparatus for recording and/or reproducing information in or from a recording medium, for example, a magneto-optical disk, a write-once optical disk, a phase change optical disk, a CD-ROM, a digital video disk (DVD), or an optical card.
2. Description of the Related Art
In recent years, a three-dimensional optical recording medium has come to light as one of promising super high-recording density optical recording media that are of a new generation succeeding the generation of such optical recording media as a magneto-optical disk, a write-only disk, a phase change disk, a CD-ROM, a DVD, and an optical card.
The conventional optical recording media are designed to have information recorded two-dimensionally on a recording layer. In contrast, when it comes to the three-dimensional optical recording medium, information is not only recorded two-dimensionally (on a planar basis) on a recording layer whose thickness is larger than a depth of focus offered by a laser, but also recorded in the depth direction of the recording layer. Therefore, if information is recorded on one hundred strata in the depth direction in the three-dimensional recording medium, a recording density that is one hundred times larger than a currently available recording density can be attained readily.
Study reports on such a three-dimensional optical recording medium have been carried in, for example, a collection of notes (P.39-P.40) prepared for lectures given at the 1992 Symposium of the Association of Optics in Kyoto, Japan and a collection of notes (29p-B-11 and 29p-B-12) prepared for lectures given at the 40th Meeting of the Japan Society of Applied Physics and Related Societies. However, the reported recording media are not intended to record or reproduce information in the form of a disk.
Moreover, for example, Japanese Unexamined Patent Publication No. 4-301226 has described an information recording/reproducing apparatus for recording and/or reproducing information in or from a disk-like optical recording medium having a guiding surface and a plurality of recording surfaces.
According to the prior art, two beams are employed, that is, a guiding beam to be irradiated to the guiding surface and a scanning beam to be irradiated to the plurality of recording surfaces. Two spots of the beams formed on the optical recording medium are advanced in a direction orthogonal to a direction of focus. Thus, the scanning beam is guided and information is recorded or reproduced. The guiding beam is positioned on a guiding track, while the scanning beam is positioned on a recording track on any of the plurality of recording surfaces.
Since the scanning beam must be positioned on any of the plurality of recording surfaces, the prior art employs a direction-of-optical axis shifter 104 composed of, as shown in FIG. 14, lenses 101 and 102 and a correcting element 103. Specifically, the lens 102 is moved along an optical axis in order to control the position of the scanning beam relative to the guiding beam in the direction of the optical axis.
Furthermore, the aforesaid patent publication has described an apparatus for recording or reproducing information by positioning a light spot on each of multiple recording layers of an optical recording medium. When this kind of optical recording medium is used for multilayer recording, the lens 102 is moved along an optical axis of an optical system including the lens to a position optimal for each recording apparatus. Assume that the focal length of an objective lens through which light forming a spot is irradiated to the optical recording medium is 3 mm and the focal length of the lens is 12 mm. In this case, an interlayer space between adjoining ones of the multiple recording layers shall be 10 xcexcm and the number of multiple recording layers shall be ten. For causing the light spot to sweep the ten layers, the lens must be moved a length calculated as 9 layersxc3x9710 xcexcmxc3x97(12/3)2=1440 xcexcm.
As a supporting device for the lens 102, a device for supporting the lens using two parallel cantilevered plate springs is generally adopted. When this kind of supporting device is employed, if the lens is moved along the optical axis, the springs loosen. This causes a movable assembly to move in a direction in which the springs are extended. Consequently, the lens 102 is displaced perpendicularly to the optic axis of the lens 101 in the direction of extension of the springs. The ray axis of light emitted from the lens 102 slopes in the direction of extension of the springs. This poses a problem in that the position of the scanning beam relative to the guiding beam on a recording medium is changed in a direction orthogonal to the ray axis of the scanning beam.
For minimizing the change in the relative position, the springs should have a sufficiently large length. However, this leads to an increase in the size of the supporting device.
An object of the present invention is to provide an optical element supporting device for information recording/reproducing apparatuses. The optical element supporting device is designed so that when an optical element is moved, even if the relative positions of two light spots formed through an objective lens are changed in a direction parallel to a direction of focus, a deviation of one of the light spots from the other light spot in a direction of tracking can be minimized.
According to the present invention, an optical element supporting device for information recording/reproducing apparatuses includes a light source, an objective lens, an optical element, and a support member. The light source irradiates a light beam. The light beam irradiated from the light source forms at least one light spot on a recording medium after passing through the objective lens. The optical element routes the light beam irradiated from the light source to the objective lens. The supporting member supports the optical element so that the optical element can move in a first direction. The supporting member is extended so that when the optical element is moved in the first direction, the position of the light spot in a direction of focus will be changed, and the light spot will travel in a direction substantially parallel to the recording tracks of the recording medium.